Leather-like sheets such as artificial leathers come to be accepted by consumers because of their superiority in light weight and easiness of handling to natural leathers, and have been widely used in clothes, general materials, sport goods and other products.
Known artificial leathers are generally produced by the following outlined method: making composite fibers for forming microfine fibers composed of two kinds of polymers having different solubility into staples; making the staples into a web by a card, crosslapper or random webber; needle-punching the web to form a fiber-entangled nonwoven fabric; impregnating an elastic polymer such as polyurethane into the nonwoven fabric; and then converting the composite fibers to microfine fibers by removing one component in the composite fibers to form a soft artificial leather.
As compared with the nonwoven fabrics made of short fibers, the nonwoven fabrics made of long fibers is advantageous because the production thereof does not need a set of large apparatuses such as an apparatus for supplying raw fibers, an apparatus for opening fibers and a carding machine. The nonwoven fabrics made of long fibers are also advantageous over the nonwoven fabrics made of short fibers in the strength.
It has been tried to produce the substrate of leather-like sheets from a nonwoven fabric made of long fibers. However, the substrate of the grain-finished artificial leathers on the market is made of regular fibers having a fineness of 0.5 dtex or more, and the artificial leather made of microfine long fibers is not yet on the market. This may be due to the difficulty of producing a long-fiber entangled sheet having a stable mass per unit area, the difficulty of handling the composite spun long fibers for forming microfine fibers, and the uneven product quality because of the uneven fineness and distortion of composite long fibers. In fact, if the nonwoven fabric is produced from microfine long fibers in the same method as employed in the production using short fibers, the sheet is wrinkled in the step of converting to microfine fibers, the dyeing step and other steps, to make the stable production difficult.
To remove such unevenness, proposed is a method in which long fibers are partly cut out to partly reduce the distortion (Patent Document 1). However, this method reduces the benefit of improving the strength by the long fiber length and fails to take full advantage of long fibers in some cases. Also proposed is a method in which a long-fiber nonwoven fabric is reinforced by a woven or knitted fabric to prevent the change in the shape of a composite sheet (Patent Document 2). However, the mere use of a reinforcing fabric cannot resist the relaxation of fiber distortion, to likely cause the wrinkling.    Patent Document 1: JP 2000-273769A    Patent Document 2: JP 64-20368A